CloudFormation Linter

Validate CloudFormation yaml/json templates against the CloudFormation spec and additional checks. Includes checking valid values for resource properties and best practices.

Warning

This is an attempt to provide validation for CloudFormation templates properties and their values. For values things can get pretty complicated (mappings, joins, splits, conditions, and nesting those functions inside each other) so its a best effort to validate those values but the promise is to not fail if we can't understand or translate all the things that could be going on.

Serverless Application Model

The Serverless Application Model (SAM) is supported by the linter. The template is transformed using AWS SAM (https://github.com/awslabs/serverless-application-model) before the linter processes the template.

Install

Command line

From a command prompt run python setup.py clean --all then python setup.py install

Pip Install

pip install cfn-lint. You may need to use sudo.

Uninstall

If you have pip installed you can uninstall using pip uninstall cfn-lint. You may need to manually remove the cfn-lint binary.

Editor Plugins

There are IDE plugins available to get direct linter feedback from you favorite editor:

Configuration

Command Line

From a command prompt run cfn-lint <path to yaml template> to run standard linting of the template

Parameters

Optional parameters:

Command Line	Metadata	Options	Description
-h, --help			Get description of cfn-lint
-t, --template		filename	Alternative way to specify Template file path to the file that needs to be tested by cfn-lint
-f, --format	format	quiet, parseable, json	Output format
-l, --list-rules			List all the rules
-r, --regions	regions	[REGIONS [REGIONS ...]]	Test the template against many regions. Supported regions
-b, --ignore-bad-template	ignore_bad_template		Ignores bad template errors
-a, --append-rules	append_rules	[RULESDIR [RULESDIR ...]]	Specify one or more rules directories using one or more --append-rules arguments.
-i, --ignore-checks	ignore_checks	[IGNORE_CHECKS [IGNORE_CHECKS ...]]	Only check rules whose ID do not match or prefix these values. Examples: - A value of `W` will disable all warnings - `W2` disables all Warnings for Parameter rules. - `W2001` will disable rule `W2001`
-d, --debug			Specify to enable debug logging
-u, --update-specs			Update the CloudFormation Specs. You may need sudo to run this. You will need internet access when running this command
-o, --override-spec		filename	Spec-style file containing custom definitions. Can be used to override CloudFormation specifications. More info here
-v, --version			Version of cfn-lint

Metadata

Inside the root level Metadata key you can configure cfn-lint using the supported parameters.

Metadata:
  cfn-lint:
    config:
      regions:
      - us-east-1
      - us-east-2
      ignore_checks:
      - E2530

Precedence

cfn-lint applies the configuration from the CloudFormation Metadata first and then overrides those values with anything specified in the CLI.

Examples

Basic usage

cfn-lint --template template.yaml

Test a template based on multiple regions

cfn-lint --regions us-east-1 ap-south-1 --template template.yaml

E3001 Invalid Type AWS::Batch::ComputeEnvironment for resource testBatch in ap-south-1

Integrate Linter (API)

Apart from CLI usage, cfn-lint can also be integrated in existing code. See the integration documentation on how to integrate cfn-lint in your own code.

Rules

This linter checks the CloudFormation by processing a collection of Rules, where every rules handles a specific function check or validation of the template.

This collection of rules can be extended with custom rules using the --append-rules argument.

More information describing how rules are set up and an overview of all the Rules that are applied by this linter are documented here

Customize specifications

The linter follows the CloudFormation specifications by default. However, for your use case specific requirements might exist. For example, within your organisation it might be mandatory to use Tagging.

The linter provides the possibility to implement these customized specifications using the --override-spec argument.

More information about how this feature works is documented here

Credit

Will Thames and ansible-lint at https://github.com/willthames/ansible-lint

License

LukasMusebrink/cfn-python-lint

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